It has been common in the past to use truck-mounted or trailer-mounted vacuum cleaning systems to clean up a wide variety of debris such as from sewers, sludge basins and waste collection areas of mills and other industrial sites. Typically, such vacuum cleaning systems have one or more tanks or collection chambers on the vehicle into which the material is deposited. A high velocity blower generates a stream of air to flow through a flexible hose that induces the waste material or debris to flow from the waste site through the flexible hose to a large collection chamber where the heavier debris is collected. The debris remaining in the air stream moves with the air stream through one or more collection chambers that collect the lighter particles of debris. Ideally, the air exhausted from the blower to the atmosphere is so clean that no contaminants are discharged to the atmosphere. When these tanks or containers become loaded with the waste material, it can be time consuming and expensive to remove the material from them and to properly off-load the material into other collection containers or into collection areas.
Various efforts have been made in the past to address this problem of removing collected debris from the vacuum cleaning system. For example, it has been common to provide truck mounted vacuum cleaning systems having a storage tank which may be raised or tilted, in the manner of a dump truck, to dump the material from the collection tank into a secondary transport vehicle or into a dump or storage site. Examples of prior art portable vacuum cleaning systems with tiltable dump features are disclosed in U.S. Pat. Nos. 4,218,226, 4,227,893 and 4,578,840.
Other arrangements provide a collection tank on the vehicle which may be raised up to allow a secondary vehicle to be positioned under the collection tank and to allow the waste material then to be transferred from the collection tank by gravity to the secondary vehicle for final transport. Examples of this type structure are disclosed in U.S. Pat. Nos. 4,121,915 and 4,574,420. These arrangements generally provide a vertical, planar range of movement of the collection tank and are illsuited for discharging the collected material outside of that vertical plane. Furthermore, these types of arrangements generally provide movement for a primary collection tank. If the tank is large, it is effective for hauling the material to a remote site, but because of the added bulk may require a costly or bulky lifting frame. On the other hand, if the liftable primary tank is small, it is easily lifted but the reduced capacity may render it inefficient for transporting material to a remote dump site.
Many collection systems include filter bags for filtering out the material from the airstream induced by the vacuum system. These filter bags become clogged quickly and must be cleaned frequently. If the operation of the blower must be terminated for cleaning of the filter bags, the effective usefulness of the system is limited. Prior art solutions to this problem generally provide an air purge system for periodically delivering a charge of compressed air to the filter bags in a direction opposite to the normal flow of air through the filter bags caused by the vacuum system without terminating the operation of the blower. In a typical prior art air purge system, there are a large number of filter bags and there are a number of air purge circuits for cleaning several of the bags at one time, with the circuits being controlled by solenoids and timer valves so that the air charge is introduced into one group of filter bags and then into another group of filter bags and then into a third group of filter bags, and so on in sequence. This sequential "stepping through" the filter bags has the disadvantage of requiring a multiplicity of control circuits including solenoid valves and control timers. This added complexity often leads to diminished reliability and is expensive in its implementation.
Accordingly, it has been determined that a need exists for a portable vacuum cleaning system which is of simple construction and yet which is self-cleaning, versatile and reliable and which provides improved access for discharging the collected material into small containers, such as 55-gallon drums and pickup truck beds as well as into large containers or dumps.